1. Field of the Invention
The field of the invention relates to novel fiber forming Poly[N,N'-(alkyl or aryl)-bis(4,4'-phthalimido)-1,3,4-oxadiazole-2,5-diyls] hereinafter referred to as PBOs.
In the prior art, the article by Y. Iwakura, et al., in The Journal of Polymer Science (A)3, page 45 (1965), discloses a method for the synthesis of polyoxadiazoles from hydrazine sulfate and simple diacids such as terephthalic acid. Other prior art references include the article by R. S. Jones, et al., in Journal of Applied Polymer Science, Vol. 25, pages 315-321 (1980), British Patent Specification No. 1,455,776; Canadian Patent No. 882,789; and the article by S. K. Varma, et al., Journal of Applied Polymer Science, Vol. 26, pages 571-577 (1981). The following Japanese patents further illustrate the prior art: J79,029,509-B42; J79,034,732-B47; J80,027,918-C34; and J50,037,778-W28. None of the foregoing references contemplate my novel fiber forming polyoxadiazoles.
The general objective of this invention is to provide novel fiber forming Poly[N,N'-(alkyl or aryl)-bis (4,4'-phthalimido)-1,3,4-oxadiazole-2,5-diyls] and a process for the manufacture of the PBOs from bis-imides in the presence of hydrazine sulfate using fuming sulfuric acid or polyphosphoric acid as the reaction medium. A further object is to provide fibers from PBOs having superior modulus to prior art polyoxadiazoles and also which exhibits no significant thermal decomposition at temperatures below about 300.degree. C.
I have found that novel PBOs can be formed by reacting bis-imides with hydrazine sulfate utilizing fuming sulfuric acid or polyphosphoric acid as the reaction medium. The reaction is conducted at a temperature of about 25.degree. to about 250.degree. C. A preferred temperature is 150.degree. C. for a time of 30 minutes. Generally temperatures of 100.degree. to 150.degree. C. are used at times ranging from about 15 minutes to about 4 hours. The PBOs have an inherent viscosity measured in sulfuric acid at 0.5 g/dl. Conc. at 25.degree. C. of about 0.6 to about 6.0. For fiber application, the inherent viscosity is preferred to exceed about 1.0. These PBOs have superior modulus to prior art polyoxadiazoles and also exhibit no significant thermal decomposition at temperatures below about 300.degree. C. For aliphatic groups having a carbon chain of 12 or more carbon atoms, polyphosphoric acid is the preferred reaction medium since PBOs incorporating these groups are insoluble in sulfuric acid.
It is also an objective of this invention to obtain polyoxadiazoles (PODs) that exhibit superior percent solids content at application viscosities. FIG. 1 shows the percent solids-viscosity of PODs obtained from either terephthalic acid (TA) or N,N'-(1,2-ethylenebis(4-carboxyphthalimide) (NEBC). NEBC is the PBO derived from ethylenediamine; this PBO for example gives at least twice the percent solids of the prior art POD derived from TA. This unique property gives our PBOs the advantage of preparing more massive fibers or films from a given volume of the polymer formulated in sulfuric acid.
In my process, trimellitic anhydride is reacted in a mole ratio of about 2:1 with an aliphatic or aromatic diamine to form a bis-imide. The PBOs are prepared by reacting about equal molar amounts of the bis-imide with hydrazine sulfate at a temperature of about 25.degree. C. to about 250.degree. C. in fuming sulfuric acid or polyphosphoric acid. The novel PBO's have the following structure: ##STR1## wherein R is a divalent aliphatic or aromatic radical. Suitably, when R is an aliphatic hydrocarbon, the carbon chain comprises 1 to about 12 carbon atoms. When R is an aromatic hydrocarbon radical the carbon atoms are in the range of about 6 to about 20. The preferred values for R are (CH.sub.2).sub.2 and (CH.sub.2).sub.6.
The carbon chain length and structure and the type of aromatic moieties utilized are determined by analyzing their ability to withstand attack or sulfonation of the carbon moiety. Fibers can be manufactured from PBOs in the following manner. The reaction solution, after completion of the polycondensation of the hydrazine sulfate with the appropriate bis-imide is cooled and mixed with sulphuric acid, 100 percent or concentrated until a solution with no water present has the required viscosity. (If the reaction solution has a low viscosity it may be used directly without dilution). The mixture is homogenized with stirring, and the resulting solution is filtered through an acid-proof fabric and deaerated under vacuum. The resulting spinning solution is formed into fibers using about 0 to 50 percent aqueous solution of sulfuric acid as a spinning bath. Non-washed, freshly formed fibers are oriented by stretching, for example, in air, or in a bath 0 to 50 percent aqueous sulfuric acid. A useful fiber spinning method is disclosed by R. S. Jones, et al., Journal of Applied Polymer Science, Vol. 25, 315-321 (1980).